For formal definitions of Liebig's and synergistic systems of factors the notion of individual and instant
fitness is used. We consider organisms that are under the influence of several factors
\(F_i\)  with intensities \(f_i\)  (\(i=1,...q\) ). For definiteness, assume that all the factors
are harmful (this is just the sign convention plus monotonicity assumption). AE supplied
for neutralization of \(i\) th factor is \(r_i\)  and fitness \(W\)  is a smooth function of \(q\) 
variables \(\psi _i=f_i-r_i\ge 0\) . This means that the factors are measured in the general
scale of AE units. Comparability of stressors of different nature was empirically
demonstrated and studied by [1]}. It was a strong argument for
introduction of AE. The value \(f_i- r_i= 0\)  is optimal (the fully compensated factor),
and any further compensation is impossible.
